1. Field of the Invention
The invention relates to a load distribution system that distributes loads to a plurality of file or data servers that transmit files or data that are requested by user or client stations, and to a method of load distribution for such systems.
2. Description of the Related Art
FIG. 7 shows a conventional video server system that comprises, for example, two video servers (server 1 and server 2), three client stations 3-5, and a network connection device 6. While the following description is made with reference to a video server system for purposes of illustration, it is to be noted that the problems encountered are applicable to any type file or data server system.
Conventionally, a client desiring a particular video file would directly select a video server through network connection device 6 and send a request to that video server for the transmission of the video file. However, if the load placed on the video server is already at maximum capacity, the client station cannot connect to it. For example, when all the clients 3, 4 and 5 request the transmission of a video file that is available only from the video server 1, the loads for the three clients are placed only on the video server 1, while no transmission load is placed on the video server 2. If the number of clients on the network exceeds the load capacity of the video server 1 and all these clients request the transmission of the same video file, the transmission capability of the video server 1 is exceeded, and the transmission of data by the video server 1 then becomes impossible.
Even when the same video file is available at both video servers 1 and 2, so long as selection of specific video servers is left to the client stations, all loads may accumulate at a single video server.
Given the arrangement of such a conventional video server, a problem that has arisen is that transmission requests from client stations tend to be directed to only one specific video server and thus all loads are placed on that server. Further, this problem cannot be resolved merely by increasing the number of video servers.
The client stations may perform a process for distributing loads over a plurality of video servers. However, in order to do this, all the client stations must have information regarding the load states at the individual video servers, and if the distribution of server loads is performed by the client stations, processing time at the client stations and the load placed on the network will be increased.
When a specific video file is frequently employed, the video file may be copied to a plurality of video servers in order to increase the transmission throughput for the video file in the system. However, if such copying is performed many times, available disk space is reduced, and video files that are less frequently used must be deleted to free up disk space. Consequently, a problem has arisen in that additional manpower is required for the accomplishment of management functions, such as the copying and deletion of files.
This invention solves the above-described problems. It is one object of the invention to provide a load distribution system for a plurality of servers whereby the loads placed on CPUs and networks, and the number of disk accesses or the loads placed on the disk-accessing capacities of the servers are distributed. It is another object of the invention to provide a method for load distribution over a plurality of servers to eliminate the problems encountered with the conventional systems.
A load distribution system according to one aspect of the invention comprises a plurality of servers, each having a memory device which stores data sets, for transmitting the data sets to a plurality of client stations; and a control server connected to the plurality of servers, the control server including a calculation device for acquiring a count of data sets that are transmitted by the plurality of servers, and a determination device for receiving transmission requests from the plurality of client stations, and for selecting, as a data transmission server, that server for which a transmitted data set count, which is acquired by the calculation device, is smallest among all the servers.
A load distribution system according to another aspect of the invention comprises a control server which includes a calculation device for calculating bandwidths that indicate a bit count per unit of time for data that are transmitted by each of the plurality of servers, and a determination device for receiving from the client stations transmission requests for the data, and for selecting, as a data transmission server, that server which has, for the bandwidths that are acquired by the calculation device, a sum that is smallest among all the servers.
According to yet another aspect of the invention, a load distribution method for a plurality of data servers includes a calculation step of acquiring counts of data that are transmitted by the servers to client stations, and a decision step of receiving transmission requests for the data from the client stations, and selecting as a data transmission server that server for which a count of data that are transmitted is smallest.
A load distribution method according to still another aspect of the invention comprises a calculation step of acquiring bandwidths that each indicate a bit count per unit of time for data that are transmitted to client stations by a plurality of servers, and a decision step of receiving transmission requests for the data from the client stations, and selecting, as a data transmission server, a server that has a bandwidth sum that is smallest.
Other objects and advantages of this invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific embodiment are given by way of illustration only since various changes and modifications within the spirit and scope of the invention will become apparent to the those skilled in the art from this detailed description.